Sound absorber

ABSTRACT

A sound absorber, especially for aerodynamic installations, comprising a tubular-like housing closed at each end by a cover member, each said cover member leaving free a central throughpassage opening. Two dampening systems are housed within the housing, one such dampening system extending as a longitudinal dampening device over the housing inner wall, the other dampening system being formed by partition walls located perpendicular to the throughflow direction and distributed over the length of the housing. These partition walls only cover a part of the internal compartment of the housing left free by the longitudinal dampening device.

United States Patent 1191 Appl. No.1 264,209

Foreign Application Priority Data June 24, 1971 Germany 2131410 US. Cl.181/42, 181/33 HB, 181/48 Int. Cl. F0ln l/04 Field of Search.. 181/50,33 H, 33 HB, 33 HA, 181/47 R, 57, 42, 71, 41, 48, 49, 59

Vasiljevic Feb. 12, 1974 SOUND ABSORBER 2,326,612 8/1943 Bourne l8l/48[76] Inventor: Costa Silard vasiljevic 3,142,354 7/1964 Kammerer et al.181/50 X Hausserstrasse l 14, Tubingen, FOREIGN PATENTS OR APPLICATIONSGermany 782,848 6/1935 France 181/59 '[22 Filed: June 19, 1972 PrimaryExaminer-Stephen J. Tomsky Assistant Examiner-John F. Gonzales u Alto ley, Agent, or Firm Werner W. Kleeman [57] ABSTRACT A sound absorber,especially for aerodynamic installations, comprising a tubular-likehousing closed at each end by a cover member, each said cover memberleaving free a central throughpassage opening. Two dampening systems arehoused within the housing, one such dampening system extending as alongitudinal dampening device over the housing inner wall, the otherdampening system being formed by partition walls located perpendicularto the throughflow direction and distributed over the length of thehousing. These partition walls only cover a part of the internalcompartment of the housing left free by the longitudinal dampeningdevice.

16 Claims, 10 Drawing Figures PAINIE FEB 1 21974 SHEET 2 OF 5PAIENTEDFEB 1' 2: 3.79 1 Ass SHEET 3 BF 5 PAJENIEU FEB-1 21974 SHEET 5OF 5 F/Q 10 v (HERTZ) SOUND ABSORBER BACKGROUND OF THE INVENTION Thepresent invention relates to a new and improved construction of soundabsorber or sound dampening device, especially for aerodynamicinstallations, and comprises a tubular-like housing closed at each endby a cover member which in each case leaves free a central throughflowopening.

Sound absorbers for aerodynamic installations must be designed inconsideration of their free throughflow cross-section such that the flowvelocity and pressure drop are as small as possible. The effectivedampening region should begin at approximately 200 Hz and should be verywide-band.

In order to fulfill these requirements it is generally necessary toprovide internally of the sound absorber housing special installations.This is especially so when thecross-section of the housing is circular,oval or quadratic, i.e., only slightly rectangular.

The prior art is already familiar with constructions of sound absorbershaving installations arranged inter nally of the housing. A tube formedof perforated sheet metal and filled with a sound-absorbing material ismost often used. Such perforated sheet metal tube is preferably employedfor coaxial mounting in sound absorbers of circular cross-section.Furthermore, it is known in this particular field of technology toarrange internally of a sound absorber a spiral-shaped coiled metalsheet of a length corresponding to the sound absorber, that is to sayhaving a number of coils. With this known type of installation there isnot realized any sound dampening effect at the low-frequency region andonly a very slight dampening effect is obtained at the middle frequencyregion. At best the sheet metal spiral is effective at thehigh-frequency region, namely by impeding the so-called sound radiation.However, it has the'additional drawback that with respect to the airthroughflow there is produced a superimposed spin flow and aconsiderable additional pressure loss.

SUMMARY OF THE INVENTION Accordingly, from what has been explained aboveit should be apparent that this particular field of technology is stillin need of sound absorbers which are not associated with theaforementioned drawbacks and limitations of the state-of-the-artproposals. Therefore, it is a primary object of the present invention toprovide a new and improved construction of sound absorber which is notassociated with the aforementioned disadvantages of the heretoforediscussed proposals and which effectively'and reliably fulfills theexisting need in the art. i

Another and more specific object of the present invention relates to anew and improved construction of sound absorber which avoids thedrawbacks of the prior art sound absorbers and, in particular, aims atthe provision of special installations for the interior of the soundabsorber which are capable of realizing up to the middle-frequencyrange, that is up to the third octave band a high sound dampening actionindependent of the dampening devices along the periphery and extensivelyindependent of the parameter U/F.

According to a particular manifestation of the inven tion it is afurther object to almost completelysuppress the so-called soundradiation, especially for sound absorbers with an unfavorableU/F-parameter, bythe provision of suitably designed installationsarranged internally of the sound absorber.

Yet a further significant object of the present invention relates to anovel construction of sound absorber, the frequency range of whichencompasses higher sound absorption of at least five octaves.

Now, in order to implement these and still further objects of theinvention, which will become more readily apparent as the descriptionproceeds, the invention contemplates accomodating two dampening systemsinternally of the sound absorber housing. One of the dampening systemsextends in the form of a longitudinal dampening device over the innerwall of the housing and the other dampening system is formed bypartition walls arranged perpendicular to the direction of throughflowand distributed over the length of the housing.- The partition wallsonly cover a portion of the internal compartment of the housing which isleft free by the longitudinal dampening device.

According to the invention both dampening systems are constructedaccording to the principle of a resona tor. The partition walls,together with the freeremaining partial cross-sections and the partialhollow compartments located between the partition walls, form a low-passresonator. Moreover, with the crosssection of the housing constant overthe length of the sound absorber the partition walls distributed .overthe length of the housing are arranged at the same spacing y from oneanother. The housing cross-section which is left free by the partitionwalls approximately corresponds to the throughflow surface of theconnection opening of the sound absorber at the housing covers.

The partition walls can be in the form of ring-shaped or annular discsmounted in the housing and which in each instance exhibit an innerthroughflow opening, or these partition walls are in the form of surfacediscs which are arranged at the central axis of the housing and fixedrelative to the housing and fixed relative to the housing wall bysupports. Finally, the partition walls can be interconnected orsupported by supports extending through the lengthwise axis of thehousing. For each meter of sound absorber at least five such typepartition walls can be advantageously employed.

If the partition walls are constructed as ring-shaped discs then thereis realized a preferred constructional manifestation of the soundabsorber which acoustically strives for a low-pass like resonatordampening action and aerodynamically realizes a very favorable pressureloss.

If, on the other hand, the partition walls are designed as surface discsarranged at the center of the housing, then, the outer diameter thereofshould correspond approximately to the inner diameter of the connectionopenings at the covers; the outer diameter can be however somewhatsmaller. Not only is there thus realized partition walls are coveredwith a sound-absorbing material, for instance mineral wool, foamedplastic, just to mention a few suitable materials. However, it isequally possible to also fill the intermediate compartments between thesuccessive partition walls with soundabsorbing material. At the inletside pressure losses are avoided by an appropriately arranged inflowlining 'which is located at the forwardmost partition wall.

Moreover, the partition walls can be molded components formed of metal,plastic, especially formed plastics or the like.

A further advantage of the invention is realized in that for theconstruction of the dampening system there are formed resonator insertsfabricated from plastic and which exhibit the shape of a box open at oneside with throughpassage openings at the bottom or floor. Theseresonator inserts are advantageously arranged such that their open sideconfronts the housing inner wall and the partition walls.

A particularly advantageous construction of sound absorber can berealized if the housing inner wall is covered with resonator insertsarranged in a row closely following one another and which are directedinwardly by means of their perforated floor. Moreover, the resonatorinserts are covered by a continuous layer of sound-absorbing material(mineral wool) which is retained by a rigid grid, sieve or the like. Theinner dampening system can either consist of partition walls formed orring-shaped discs and covered with a mineral wool layer, the partitionwalls merging with the longitudinal dampening device, or there can beused partition walls in the form of circular discs located at thecentral axis of the sound absorber housing and which, in turn, togetherwith the sound-absorbing'material arranged thereon or therebetween areenclosed by a sieve, grid or the like and supported in the center of thehousing by suitable supports, struts or the like. A particularly goodeffect also can be then realized if the resonator inserts are covered attheir open side confronting the inner wall of the housing by a plasticfoil or the like. Fabrication of the inventive sound absorber issimplitied in that both dampening systems are manufactured aspre-fabricat'ed units and each for itself or conjointly can be insertedfrom the head'end into the tubular-like housing.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be betterunderstood and objects other than those set forth above, will becomeapparent when consideration is given to the following detaileddescription thereof. Such description makes reference FIG. 6 is across-sectional view of the arrangement of FIG. 5, taken substantiallyalong the line VIVI thereof;

FIG. 7 is a perspective view of a resonator insert;

FIG. 8 is a cross-sectional view of the arrangement of FIG. 7, takensubstantially along the line VIII-VIII thereof;

FIG. 9 is a cross-sectional view of the arrangement of FIG. 7, takensubstantially along the line IX-IX thereof; and

FIG. 10 is a graph explaining the mode of operation of the soundabsorber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now thedrawings, the inventive sound absorbers or sound-dampening devicesgenerally possess a tubular-like or pipe-like housing 1 which maypossess a round, oval or quadrangular cross-section and closed at itsends by the covers or cover members 2 which, in turn, each possess acentral throughflow opening 3. Each such throughflow opening 3 can beadvantageously provided with a flange 3a for connection to other pipeconduits. Internally of the housing 1 there is provided a longitudinaldampening device 4 which can be constructed either according to theabsorptionprinciple, but most preferably according to the resonatorprinciple. The longitudinal dampening device 4 is covered and supportedin the housing 1 at the inside by means of a sieve cylinder or by meansof a grid, perforated sheet metal or the like, as generally indicated byreference numeral 5.

Now with the embodiment of sound absorber of the type depicted in FIG. 1partition walls 6 are distributively arranged at a uniform spacing fromone another throughout the length of housing 1. Each of. these partition walls 6 exhibits a central throughflow opening 7 which isapproximately equal in surface area to the connection openings 3 at thehousing covers 2. At the edge of each of the throughflow openings 7 theillustrated ring-shaped discs forming such partition walls 6 areprovided with flexed or bent portions 8 disposed in the direction ofthroughflow. As clearly seen by referring to FIG. 1 the partition walls6 are covered with a sound-absorbing material 9, for instance mineralwool, at the region of the hollow compartment bounded by the flexedportions 8. The partition walls 6 are advantageously fixedly seated atthe sieve or perforated sheet metal member 5. They form together withthe longitudinal dampening device 4 an-insert unit which can be pushedinto the housing 1 from the head end thereof. What is decisive for themagnitude of the upper boundary frequency of the low-pass like dampeningis the magnitude of the partial hollow compartment H between thepartition walls in relation to the square of the radius of thethroughpassage opening 7.

With the embodiment of sound absorber of the type depicted in FIG. 2 thepartition walls are formed by circular discs 11 which are coaxiallyarranged at the same spacing from one another at the interior of thehousing 1 lined with the longitudinal dampening device 4, 5. The discs11 have marginal flexed portions 13 and are covered with asound-absorbing material, for instance mineral wool 14, at the sideconfronting the outlet pr exit, as shown. The discs 11 are retained bymeans of struts 10 piercingly inserted through the housing 1 andsupported at the lateral covers 2. At the inflow side the forwardmoststrut 11 is provided with an inflow lining 12 for reducing the pressureloss.

The direction of flow is marked by arrows both in the arrangement ofFIG. 1 and also in the arrangement of FIG. 2.

Now in FIGS. 3 and 4-there is illustrated an improved version of thesound absorber of the type depicted in FIG. 1. The partition walls 6 arecovered and connected with one another at the inside by means of asieve, grid, perforated sheet metal or the like, as generally indicatedby the reference character 15. In this connection the space between thepartition walls 6 can be also filled with a suitable sound-absorbingmaterial 16.

In order to ensure for a good dampening action for the longitudinaldampening system there are employed resonator inserts 17, as such havebeen illustrated in detail in FIGS. 7 to 9. These inserts 17 entirelyconsist of foamed plastic, such as for instance styropor. Theyessentially possess a box-like configuration, and compartments areformed by transverse walls 18 and longitudinally extending walls 19 andwherein the floor 21 has a somewhat larger thickness and is equippedwith a multiplicity of openings 22 arranged in rows behind and adjacentone another.

In order to facilitate assembly of the resonator inserts 17 into aring-shaped lining there are provided at one side of the floor the beads23 or recesses 24.

From the arrangement of FIGS. 3 and 4 it will be recognized that theresonator inserts 17 are mounted in the housing 1 behind and neighboringone another with their open side facing towards the outside. A coverfoil 25 covers the resonator compartments 20 at their open side Theresonator inserts introduced as a lining into the housing 1 are finallycovered with a sound-absorbing layer 26 formed of mineral wool or thelike and retained by the cylindrical sieve, grid or equivalentstructure, generally indicated by reference character 5.

Now in FIGS. 5 and 6 there is illustrated an improved version of soundabsorber of the type shown in FIG. 2. Just as was previously the case,here also the longitudinal dampening system is formed by resonatorinserts. on the other hand, the inner dampening device consists ofce'ntrally'arranged circular discs 1 1 forming the partition walls, assuch have already been used for the embodiment of sound absorber of FIG.2. The inner sound absorber is enclosed as a unit by a sieve cylinder 27and is retained by means of the discs 28 at the housing, andspecifically at the sieve jacket 15.

With the inventive constructions of sound absorbers there is realized,among other things, the advantage that with the internally arrangedresonator sound can be effectively dampened in a low-pass like manner atleast up to the third octave region, that is into the middle-frequencyregion. Furthermore, by virtue thereof there is realized the verynotable advantage that the thickness of the longitudinal dampeningdevice can be generally considerably less than is usually the case. Withthe special constructional embodiment which contemplates the internalarrangement of the surface discs there is realized the additionaladvantage that the so-called sound radiation can be almost completelysuppressed without additional manufacturing expenditure. As a resultthere is produced a sound absorber with the important acousticaladvantage that in a frequency range of five to six octaves highdampening with approximately constant frequency course of the dampeningcan be realized.

For reasons of fabrication and especially for reasons of assembly it isfurthermore very advantageous if the inner resonator arrangement isdesigned as an independent insert unit.

Finally, the graph depicted in FIG. 10 illustrates the throughputdampening mass Db plotted over the frequency f for a tested soundabsorber designed according to the invention.

While there is shown and described present preferred embodiments of theinvention, it is to be distinctly understood that the invention is notlimited thereto but may be otherwise variously embodied and parcticedwithin the scope of the following claims.

What is claimed is:

l. A sound absorber, especially for aerodynamic installations,comprising a housing having a tubular wall defining a flow passagethere-through, said housing including an inlet end and an outlet end,each of said ends being partially closed by covers having throughflowopenings defined therein, an outer dampening system defined by aplurality of resonator inserts arranged tightly in a row behind oneanother and extending longitudinally over the inner surface of saidtubular wall, said resonator inserts having an open side and aperforated floor, said open sides facing the inner surface of said walland said perforated floors facing inwardly of said housing and coveredby a continuous layer of sound absorbing material, an inner dampeningsystem disposed coaxially with said other dampening system and partiallyobstructing said flow passage, said inner dampening system including aplurality of partition members distributed over the length of saidhousing and having side walls extending transversely of said flowpassage and facing said inlet and outlet ends, and sound absorbingmaterial covering said side wall of each of said partition members whichfaces said outlet end.

2. The sound absorber as defined in claim 1 wherein each cover has anopening defining a connection opening forming a throughflow area, andwherein the crosssection area of the flow passage left unobstructed bythe partition members approximately corresponds to the throughflow areaof the connection opening at the housing covers.

3. The sound absorber as defined in claim 2, wherein said partitionmembers comprise a number of ringshaped discs inserted into the housing,each of said ring-shaped discs having an internal throughflow open- 4.The sound absorber as defined in claim 2, wherein said partition memberscomprises surface discs which are arranged at the central axis of thehousing, and support means for supporting such surface discs relative tothe wall of the housing.

5. The sound absorber as defined in claim 1, further including supportmeans extending in the direction of the lengthwise axis of the housingfor interconnecting and positionally retaining said partition members.

6. The sound absorber as defined in claim 5, wherein said partitionmembers have edges confronting sound throughflow, said partition memberedges being flexed in the direction of sound throughflow.

7. The sound absorber as defined in claim 1, wherein saidsound-absorbing material is mineral wool.

' of the sound absorber are provided with an inflow lining reducingpressure losses.

11. The sound absorber as defined in claim 10, wherein said partitionmembers comprise molded components.

12. The sound absorber as defined in claim 1,

shaped discs which merge with support means for the resonator insertsand the sound-absorbing material.

13. The sound absorber as defined in claim 1,

wherein the partition members form circular discs lowherein thepartition members are in the form of ringcated substantially at theaxial center of the sound absorber housing, means for enclosing saidcircular discs together with the sound-absorbing material, and supportmeans for securing the circular discs at the center of the housing.

14. The sound absorber as defined in claim 1, further including aplastic foil for covering the resonator inserts at their open sideconfronting the inner surface of the housing wall.

15. The sound absorber as defined in claim 1, wherein both dampeningsystems are constructed as pre-fabricated units each of which can beindividually or collectively inserted from one end of the housing intosuch housing.

16. The sound absorber as defined in claim 1 wherein each of saidresonator inserts is defined by a box, and wherein said open side andsaid perforated floor comprise opposite sides of said bort.

1. A sound absorber, especially for aerodynamic installations,comprising a housing having a tubular wall defining a flow passagethere-through, said housing including an inlet end and an outlet end,each of said ends being partially closed by covers having throughflowopenings defined therein, an outer dampening system defined by aplurality of resonator inserts arranged tightly in a row behind oneanother and extending longitudinally over the inner surface of saidtubular wall, said resonator inserts having an open side and aperforated floor, said open sides facing the inner surface of said walland said perforated floors facing inwardly of said housing and coveredby a continuous layer of sound absorbing material, an inner dampeningsystem disposed coaxially with said other dampening system and partiallyobstructing said flow passage, said inner dampening system including aplurality of partition members distributed over the length of saidhousing and having side walls extending transversely of said flowpassage and facing said inlet and outlet ends, and sound absorbingmaterial covering said side wall of each of said partition members whichfaces said outlet end.
 2. The sound absorber as defined in claIm 1,wherein each cover has an opening defining a connection opening forminga throughflow area, and wherein the cross-section area of the flowpassage left unobstructed by the partition members approximatelycorresponds to the throughflow area of the connection opening at thehousing covers.
 3. The sound absorber as defined in claim 2, whereinsaid partition members comprise a number of ring-shaped discs insertedinto the housing, each of said ring-shaped discs having an internalthroughflow opening.
 4. The sound absorber as defined in claim 2,wherein said partition members comprises surface discs which arearranged at the central axis of the housing, and support means forsupporting such surface discs relative to the wall of the housing. 5.The sound absorber as defined in claim 1, further including supportmeans extending in the direction of the lengthwise axis of the housingfor interconnecting and positionally retaining said partition members.6. The sound absorber as defined in claim 5, wherein said partitionmembers have edges confronting sound throughflow, said partition memberedges being flexed in the direction of sound throughflow.
 7. The soundabsorber as defined in claim 1, wherein said sound-absorbing material ismineral wool.
 8. The sound absorber as defined in claim 1, wherein thesound-absorbing material is foamed plastic.
 9. The sound absorber asdefined in claim 1, wherein the partition members are spaced from oneanother so as to define therebetween intermediate compartments, andsound-absorbing material filling such intermediate compartments.
 10. Thesound absorber as defined in claim 9, wherein the partition member wallsfacing the inlet end of the sound absorber are provided with an inflowlining reducing pressure losses.
 11. The sound absorber as defined inclaim 10, wherein said partition members comprise molded components. 12.The sound absorber as defined in claim 1, wherein the partition membersare in the form of ring-shaped discs which merge with support means forthe resonator inserts and the sound-absorbing material.
 13. The soundabsorber as defined in claim 1, wherein the partition members formcircular discs located substantially at the axial center of the soundabsorber housing, means for enclosing said circular discs together withthe sound-absorbing material, and support means for securing thecircular discs at the center of the housing.
 14. The sound absorber asdefined in claim 1, further including a plastic foil for covering theresonator inserts at their open side confronting the inner surface ofthe housing wall.
 15. The sound absorber as defined in claim 1, whereinboth dampening systems are constructed as pre-fabricated units each ofwhich can be individually or collectively inserted from one end of thehousing into such housing.
 16. The sound absorber as defined in claim 1wherein each of said resonator inserts is defined by a box, and whereinsaid open side and said perforated floor comprise opposite sides of saidbox.